Taurine (2-aminoethanesulfonic acid) is a potent antioxidant and inhibits cell apoptosis in ischemic reperfusion injury. In this study we evaluated whether addition of taurine to St. Thomas' cardioplegic solution enhances its myocardial protective effects in prolonged hypothermic heart preservation in rats. Hearts isolated from male Sprague-Dawley rats were mounted on a Langendorff apparatus to estimate baseline cardiac function, then arrested and stored in St. Thomas' cardioplegic solution, with taurine (10 mM; taurine group, n = 8) or without taurine (control group, n = 8), for 6 h at 4 degrees C. After storage, the hearts were reperfused and heart rate (HR), coronary flow (CF), left ventricular developed pressure (LVP), and positive maximum left ventricular developing pressure (max LV dp/dt) were measured. The LV tissue was examined immunohistochemically for determining DNA oxidative stress and cell apoptosis. Compared with control groups, recovery of LVP (P < 0.001), max LV dp/dt (P < 0.001), and coronary flow (P < 0.001) were significantly enhanced, whereas glutamic oxaloacetic transaminase (P < 0.01), lactate dehydrogenase (P < 0.05), creatine phosphate kinase (P < 0.01), 8-hydroxy-2'-deoxyguanosine index (P < 0.01), caspase-3 mRNA expression (P < 0.05), and percentage of TUNEL-positive cardiomyocytes (P < 0.05) were reduced in the taurine group. Addition of taurine to St. Thomas' cardioplegic solution improved cardiac function recovery for prolonged hypothermic rat heart preservation by suppressing DNA oxidative stress and cell apoptosis.